This invention relates to a method of and apparatus for controlling machinery capable of forming, filling and sealing packages, and more particularly, control of sealing and cutting functions of such machinery.
Package forming, filling and sealing machinery of the type, for example, in which flexible packaging material is formed into tubing, and heat-sealed at package length intervals by means of a pair of sealing members or jaws to cut the tubing at each seal to provide a trailing or upper end seal for each package being completed and a leading or lower end seal for the next package, have been known for many years.
Functions such as knife motion and impulse control in these machines have been under the control of a limit switch mounted in the jaw area which sensed actual closure of the jaw assembly, thus enabling the function only if the dies were securely closed. This action prevented a function such as a knife from operating if the jaws were not closed.
For years, many attempts have been made at designing and perfecting a jam detection scheme to prevent injury to the operator or damage to the sealing surfaces should product being packaged or other foreign object get caught in the sealing area. All these schemes involved forming a "window" with a cam or other timing device which required the jaws to be closed at a certain point in the machine cycle or the jaws would open in the event of a jam. Unfortunately, the system was unreliable for several reasons.
For example, as the system went from a cold start to normal ambient operating conditions, the jaw closed point in machine degrees shifted so the jaws closed point occurred earlier in the cycle, thus requiring the "window" to be moved a corresponding amount earlier to still provide protection. This was a nuisance and operators typically moved the window very late in the cycle, thus defeating the purpose of the detector.
Also, the system had to be adjusted for each bag size and was simply regarded as a nuisance adjustment. Further, since the jaw close function is pneumatic in nature, the settings would not repeat due to regulator adjustments or air pressure variations, again causing the system to run with an oversized "window" to compensate for system constraints. In addition, timing could be adjusted in terms of start and stop initiation points, but since the jaw closed point was not directly linked to the machine motion for the reasons cited above, the jaw closed point in machine degrees was unknown. This affected the quality of end seals due to inconsistent jaw closed duration.